How flexible is the size of Mold Earth?

Question

The transmutation cantrip mold earth (EEPC, p. 21; XGtE, p. 162-163) explicitly states:

You choose a portion of dirt or stone [...] that fits within a 5-foot cube.

Would this indicate that the total amount of dirt or stone you can manipulate has to be to able to fit in a 5 foot cube, not necessarily that it does?

For example, one of the effects this spell can do is turn dirt/stone into difficult terrain. With this spell, could a caster turn 60 5ft. squares into difficult terrain, if they're an inch thick? If I did my maths right that total ammount of dirt could fit in a 5 foot cube.

Is this how one should read this spell? Or, does it mean you can only turn 5ft. of dirt/stone into difficult terrain, making it the equivalent of a muddy puddle one can pretty easily side step with little to no consequences?

Answer 1

fits in a 5-foot cube

Is different to having the volume of 5-feet cubed.

A steel sword that is 10 feet long, does not fit in a 5-foot cube, even if the steel used came from much less than a 5-foot cube.

There are spells that use specific wording to allow such variations of volume such as

• Wall of Fire

  up to 60 feet long, 20 feet high, and 1 foot thick, or a ringed wall up to 20 feet in diameter, 20 feet high, and 1 foot thick.

• Wall of Stone

  The wall is 6 inches thick and is composed of ten 10-foot- by-10-foot panels. Each panel must be contiguous with at least one other panel. Alternatively, you can create 10-foot-by-20-foot panels that are only 3 inches thick.

That are referenced in this similar answer.

If the rule allowed for your reading, one could effect your entire 30ft radius into difficult terrain with every cast. There would be no reason to define a 5ft cube at all. All for the price of a cantrip.

"Fits within" means it already does fit, not that you could make it fit.

Answer 2

There is no flexibility in the casting of this spell

As you stated, Mold Earth says:

You choose a portion of dirt or stone that you can see within range and that fits within a 5-foot cube.

While your maths is right, 60 one foot thick slices of soil/dirt could fit into a 5 ft cube, this spell requires a target area that already 'fits within a 5-foot cube' not that 'could fit within a 5-foot cube'.

Is there another way to exploit this cantrip to effect a larger area?

Not really, certainly not to achieve anything like the area of effect you were hoping for (60 ft.). You could effect a maximum of two 5 ft. cubes at once (10 ft.), rather than one.

The spell states:

This change lasts for 1 hour.

Assuming one action every six seconds, you could cast Mold Earth 600 times in an hour. This sounds like a fun way to pass the time in principle, when you're waiting to lay an ambush, however, abusing the cantrip in this way has been clearly ruled out:

If you cast this spell multiple times, you can have no more than two of its non-instantaneous effects active at a time.

Answer 3

The dirt/stone must (already) fit within a 5-foot cube of space

Spells do what they say they do.

The spell description says that the targeted portion of dirt/stone fits within a 5-foot cube, not that it is able to fit within such a cube given potential rearrangement.

If the spell was meant to allow you to take dirt from anywhere as long as the total volume was no larger than a 5-foot cube, it would say so... but it doesn't. The spell doesn't allow you to affect more than a 5-foot cube of space at a time. Since it's a cantrip, of course, you could cast it multiple times, but as the last line of the spell description states:

If you cast this spell multiple times, you can have no more than two of its non-instantaneous effects active at a time, and you can dismiss such an effect as an action.

In short: you can target any amount of dirt that is already contained within a 5-foot cube of space. You can't reshape the area of effect of a single casting of the spell. You can cast it multiple times to make an area difficult terrain, but since that change lasts for an hour (and is thus non-instantaneous), you can only do so twice while keeping that effect active on both targeted areas of effect.

Answer 4

While RAW suggests the source material would need to fit within the confines of a 5' cube initially, there's nothing to stop you from repeating effects.

Specifically regarding the difficult terrain option, it's clear that RAI wants to limit your effect on the battlefield to 2 "squares" of 5'x5' area. As soon as you attempted to affect a third, the first non-instantaneous effect would end. While the volume within a 5' cube allows much more total coverage, it would necessarily lay there as though naturally deposited, without much influence beyond where you placed it, and gravity.

Please note that moving earth is in fact one of this cantrip's instantaneous effects. Meaning, if you used the cantrip to move or excavate a maximum of 125 cubic feet of qualifying material, contained within a 5' cube, that material remains permanently where deposited, until removed by some means. Given a surprisingly short time, a caster of this cantrip could fortify an area of loose earth with a series of lasting mounds and trenches.

Yes, the first heavy rain would take a dramatic toll on your efforts, but in a pinch, you can practically move mountains. (Of course, mountains are rockier terrain, and immutable via mold earth.) ;P